That's where I have to wonder how anybody expected cryptocurrency in its current state to work. It certainly seems to be designed to be wasteful. A typical BTC transaction takes about an hour to process as it goes through (normally 6?) verifications... I suppose multiple verifications isn't necessarily a bad thing, but in a system doomed to fail, it doesn't help. When you consider that mining pays the miner and difficulty is built in to the system as a way to regulate itself when everyone and their grandma is doing it, it seems there's more than a simple payment network in mind.
If I can be allowed to be stupid for a moment, maybe it's like the law of equivalent exchange from Fullmetal Alchemist. You cannot create something from nothing, so you can't just invent a coin and say it's worth a million dollars, and trade it in for a million dollars. It has to garner value from somewhere. Maybe all the hardware being produced, which winds up being used for mining, and the energy going into that hardware to run it is part of its value. Yes, I know that the market value increases when actual money is dumped into it... as in, if someone bought 10,000 BTC tomorrow, the price would likely jump up quite a bit... but that doesn't seem to account for everything in my mind. If I bought those 10k BTC, who really cares? All I did was trade one currency for another. If things were a bit different, it could well be that my BTC is worthless and whoever sold it to me is laughing all the way to the bank. BTC has value because we give it value, in many ways. Buying hardware to run it and dumping energy into it is one way we give it value.
If you look at it that way, BTC is just another product. How much resources do you think it takes to build and run a steel mill, for example? Or any other factory? I always thought Cryptocurrency was made as a way to give the everyday person a little bit of that power typically held with an iron grip by banks and governments. No, it's not the most efficient thing in the world, but literally anyone can do it, and a lot of people do... a lot of regular guys like you and me. Maybe that's why it's so large, and consumes so much power... because there was a large market for it just waiting to happen.